热负荷及环境温度对机械泵驱动两相热控系统性能影响

运用传热学、流体力学、两相流和控制论等知识对机械泵驱动两相热控系统的各个部件建立混合物模型及Simulink仿真模块。借助于Matlab/Simulink计算软件,对系统进行了动态仿真计算,得到了系统分别在热负荷和冷凝器侧环境温度变化情况下的温度分布和变化情况。据此对系统进行了运行稳定性分析。结果表明蒸发器侧热负荷的阶跃变化对蒸发器出口温度影响较大,对冷凝器进出口温度影响则较小;冷凝器侧环境温度周期性变化对冷凝器出口温度、储液器入口温度及泵入口温度影响较大,对蒸发器进出口温度影响则较小。     

10MW高温气冷实验堆满功率下的动态特性研究

根据高温气冷实验堆HTR-10的运行特点和控制要求,利用清华大学核能与新能源技术研究院开发的用于仿真计算的系统——10MW HTR-10仿真控制支持系统,进行了HTR-10满功率下动态特性的仿真研究,研究了HTR-10满功率时在外加反应性、氦流量、给水流量变化下的动态特性规律,并将得出的系统动态响应的仿真结果与反应堆在3MW低功率运行时的试验结果作了比较,发现动态特性变化规律一致。验证了仿真控制支持系统的准确性,同时获得了HTR-10满功率下的主要动态特性：由于HTR-10具有很大的负温度反馈系数,只用控制棒很难调节堆功率;而氦流量的变化对堆功率影响很敏感,二者几乎成线性变化,适于负荷变化的功率调节;给水流量的变化对核功率和热氦温度等一回路的参数影响不大,但对蒸汽温度等二回路参数影响显著,适合于蒸汽温度的调节。     

根据温度变化的产品包装膜

兰德克公司的Intelimer膜的透气性可由温度调节而变化.用于产品包装的这种薄膜,符合产品的透气率,而且如事先设定温度,达到此温度,其透气性即发生变化.大部分产品的透气程度随温度变化而变化.新鲜产品的包装,因考虑到嫌气条件和高温等引起的二氧化碳伤害而设定在5℃,而现在使用的包装膜,基本上透气性不随温度而改变.兰德克公司开发出在温度细微变化时对气体透过情况能够显示出很大变化的薄膜.这种调节机制是通过利用拥有长链的脂肪族乙醇基的高分子侧链的结晶高分子技术完成的.侧链有妨碍气体分子(氧气、二氧化碳等)透过的结晶结构,如达到某特定温度则侧链溶解,变成可使气体分子透过的不定形结构.这种温度开关也可以薄膜的粘着性和粘性产生变化.     

氦气作为增压气体排出贮罐内液氢过程的CFD分析

基于计算流体力学方法,数值模拟了用常温氦气作为增压气体压出贮罐内液氢过程的流动和传热传质特性。构建了基于二维轴对称的VOF多相流以及包含氢气和氦气组分流动的气相多组分数值模型,液氢界面相变传质基于Hertz-Knudsen方程计算。分析了排出过程贮罐内压力、温度、液位及液氢相变率随时间的变化,重点考察气相出现在贮罐出口时间,以及此时气相中氦气含量。发现刚开始增压时,高温氦气和低温氢气传热只发生在氦气进口附近,贮罐内压力增加较慢,液氢界面不存在蒸发现象。随着进入氦气增加,贮罐内气相温度逐渐形成分层,在一定时刻,液面上气体温度开始上升,触发沸腾蒸发,导致压力快速增加。由于贮罐出口液体外流导致的减压效应远小于气相空间的压力增速,贮罐压力急剧增加并超过氦气入口,部分低温气体混合物从入口倒流出贮罐,同时使氦气入口处温度降低。由于贮罐内压力增加,底部液氢出口流量随时间呈线性增加。计算结果揭示了液氢贮罐增压流出过程复杂的流动和传热传质特性,对低温液体的储运有实际工程指导意义。     

翅片管式CO2气体冷却器模拟与优化

为了研究CO2在翅片管式气体冷却器内的流动特性,建立了稳态分布参数模型,并进行了实验验证。结果表明:CO2侧换热系数受入口压力和质量流量的影响较大,但入口温度对其影响很小。换热量随着入口压力的变化有一个最大值;且随着流量的增大,最大换热量所对应的入口压力值逐渐增大。压降和换热量均随入口温度的增加而线性增加。适当增加管程数,采用较小管径的气冷器性能更高。     

一种液压式连续可变压缩比技术的研究

为进一步提高发动机燃烧效率,减少发动机有害气体的排放,提出了一种液压式连续可变压缩比技术的设计方案。它是通过液压系统控制偏心销转动来改变上止点的位置,从而使燃烧室体积发生变化,实现在调节区间内任意连续可变压缩比的改变。首先,根据所设计的方案分析了其液压系统在2个不同阶段的调节工作原理;然后,利用三维软件Solidworks2010对整个系统进行三维建模,根据模型设计的具体尺寸,得到连续可变压缩比调节的范围为8.81~22.43;最后分析了不同转速下活塞系统综合力（活塞惯性力和活塞表面气体压力的合力）的变化情况,并通过MATLAB与AMESim对构建的液压系统进行了联合仿真试验,探究了不同转速下活塞系统综合力向上和向下时液压系统的流量特性和压力特性。仿真结果表明：发动机转速在中低速条件下,活塞系统调节响应迅速,具有良好的动态特性,证明该设计具有一定实用性。仿真结果为用于液压容积调节的连续可变压缩比技术的实际应用提供了理论依据,具有重要的实际指导意义。     

差压流量计的误差分析

孔板设计时是按照给定的已知条件进行计算的,但实际测量中介质的温度、密度、压力、粘度等参数往往发生变化,实际应用中被测介质温度每变化10℃,液体的密度变化大致不超过1％。气体在常温附近,温度每变化10℃时,密度变化约3％,气体在1个大气压时,压力每变化10Pa,密度变化10％,气体测量,温度压力波动时,必须进行温度压力修正。     

推进系统参数变化对液体火箭纵向振动响应的影响分析

为了优化液体火箭推进系统,避免POGO振动引起液体火箭低频振动环境恶化对火箭飞行过程的不利影响,建立了液体火箭POGO振动系统的动力学模型,利用动态灵敏度技术,提出了液体火箭纵向振动响应对推进系统参数的灵敏度时域分析模型。通过数值仿真,得到了推进系统流体惯性、阻力和刚度参数以及泵的动态增益变化对液体火箭纵向振动响应的影响规律。研究结果表明,液体火箭纵向振动响应对流体惯性和阻力参数的敏感程度比流体刚度参数明显大,泵动态增益的变化对液体火箭纵向振动响应的影响最大,泵前短管的流体刚度变化对液体火箭纵向振动响应的影响最小。为减小液体火箭纵向振动,进一步研究POGO振动特性提供参考。     

基于TRNSYS 17的表冷器水侧入口参数寻优研究

利用双回路表冷器调节水侧入口参数(冷冻水供水温度与流量)可以降低恒温恒湿空调系统的热湿补偿损失和系统能耗。基于软件TRNSYS 17搭建恒温恒湿系统仿真平台,并通过试验验证其准确性。通过调节水侧参数进行系统能耗最低点水侧参数寻优,参考显热比-冷量耦合数据平面验证寻优结果的准确性。基于最优水侧入口参数模拟四种典型工况下的部件能耗与总能耗,分析被调空间热湿负荷与最优水侧入口参数的定性关系;最后与常规恒温恒湿空调系统比较,绘制节能率分布图。结果表明:低温高湿工况的节能率最低,但不低于16.45%;高温低湿工况的节能率最高,最高达71.13%。     

工艺参数对低温液体喷射混合器混合性能的影响

为了优化液化天然气气质,探究工艺参数对低温液体喷射混合器内部流场的影响,基于不同沸点低温液体互溶混合机理,以液态甲烷、液态丙烷为工质,分析了不同工艺参数喷射混合器内两股流体的流动特性和混合效果。分析结果表明:喷射混合器的主流体入口压力、引射流体入口压力及混合流体出口压力均存在一个最优值,在考虑实际生产环境的基础上,应使其值尽可能的接近这一临界值;在其他工艺参数确定的情况下,随着引射流体入口温度的增大,喷射混合器的混合性能越好,可适当增大引射流体入口温度,以提高喷射混合器的混合性能。主流体入口压力0.22 MPa、引射流体入口压力0.1 MPa、混合流体出口压力0.1 MPa、引射流体入口温度249.15 K时,该结构喷射混合器的混合性能最好。     

An approximate method for transient behavior of finned-tube cross-flow heat exchangers

A closed, approximate, analytical approach is obtained for transient behavior of finned-tube, liquid/gas cross flow heat exchangers for the step change in the inlet temperature of the hot fluid. In this two-solid heat capacity approach, the heat capacities of the hot and cold fluids and the heat capacity of the wall and the fins are lumped separately. The temperature variation of both fluids between inlet and outlet is assumed to be linear. It is also assumed that flow rates and inlet conditions remain fixed for both fluids, except for the step change imposed on the inlet temperature of the hot fluid. Energy equations for the hot and cold fluids, fins and walls for both approaches are derived and solved analytically. The variation of the exit temperatures of both fluids with time are obtained for a step change in the inlet temperature of the hot fluid. The dynamic behavior of the heat exchanger is characterized by time constant, delay time and gain. This approach is easier to apply and can easily be modified for other heat exchanger types. Results are compared with the experimental and numerical results given in the literature.     

水冷套管式CO_2气冷器的设计及实验研究

本文设计了一台CO_2套管式气冷器并对其进行了换热特性的实验研究。该气冷器采用逆流三重套管,CO_2在内管流动,冷却水在内外管间流动。实验研究了不同CO_2质量流量、入口压力和冷却水温度对传热系数、换热量和换热器效能系数的影响。实验结果表明,随着CO_2质量流量的增加,传热系数和换热量均呈先增后减的趋势,换热器效能系数逐渐减小;CO_2质量流量不变时,传热系数、换热量和换热器效能系数均随气冷器CO_2入口压力的升高而逐渐增大;随着冷却水温度的升高,传热系数、换热量和换热器效能系数均逐渐减小。     

不同空气侧风速下微通道蒸发器换热特性实验研究

搭建微通道蒸发器性能实验台,采用控制变量法研究不同空气侧风速下微通道蒸发器表面温度分布、制冷剂进出口压力的变化规律,计算换热量和换热系数,从而分析空气侧风速对微通道蒸发器的流量分配特性和换热效果的影响。结果表明,随着风速增大,微通道蒸发器制冷剂流量分配不均匀性增大,进出口压力波动振幅和周期增加,压降增大,风速2 m/s时微通道蒸发器换热效果最佳。     

Continuous formation of slurry ice by cooling water–oil emulsion in a tube

Water-silicone oil emulsion with an additive, (C₂H₅O)₃SiC₃H₆NH₂, was examined as a heat storage material. A spiral tube used as a heat exchanger was immersed in a low temperature bath and the emulsion was circulated in the tube to make ice continuously. Ice was separated from the ice–liquid suspension in an outlet tank. The amount of formed ice, the temperatures of the inlet and the outlet of the heat exchanger, and the temperatures in the tube wall were measured and the overall heat transfer coefficient and the heat flux through the tube were calculated. Experiments were carried out, varying the flow rate, the temperature of cooling brine, and the thickness of tube wall. The condition under which slurry ice was formed continuously without adhesion of ice to the cooling wall was clarified. Though decrease in the thermal resistance of the tube increased the rate of ice formation or raised the brine temperature, it narrowed the range of the flow rate and of the brine temperature in which slurry ice was formed continuously.     

圆柱型翅片管换热器变工况传热性能模拟与分析

基于分排参数模型,本文建立了圆柱型翅片管换热器的性能仿真计算模型,对换热器的传热性能进行计算,并进行实验验证。结果表明:换热量的平均相对误差最大,为6.31%;出风干球温度的平均相对误差最小,为0.61%。计算所得各性能参数与实验值吻合良好。根据仿真模型,对不同制冷工况下的换热器进行计算,研究了循环风量、水质量流量、进风干球温度以及进水温度的变化对换热性能的影响。分析换热器的变工况特性可预测其非设计工况下的换热性能,并为换热器的运行工况调节提供依据。     

Development of a slug flow absorber working with ammonia-water mixture: part I—flow characterization and experimental investigation

This study deals with an experimental investigation for a counter-current slug flow absorber, working with ammonia–water mixture, for significantly low solution flow rate conditions that are required for operating as the GAX (generator absorber heat exchanger) cycle. It is confirmed that the slug flow absorber operates well at the low solution flow rate conditions. From visualization results of the flow pattern, frost flow just after the gas inlet, followed by slug flow with well-shaped Taylor bubble, is observed, while dry patch on the tube wall are not observed. The liquid film at the slug flow region has smooth gas–liquid interface structure without apparent wavy motion. The local heat transfer rate is measured by varying main parameters, namely, ammonia gas flow rate, solution flow rate, ammonia concentration of inlet solution and coolant inlet conditions. The heat transfer rate while absorption is taking place is higher than that after absorption has ended. The absorption length is greatly influenced by varying main parameters, due to flow conditions and thermal conditions.     

逆流填料式溶液除湿器性能的数值模拟

对溶液除湿器中传热传质过程进行热力学分析,根据除湿塔的结构及溶液与空气的流动方式,建立除湿器的热质交换物理和数学模型,模拟计算除湿器人口空气和溶液参数对除湿器出口空气参数的影响,得到各入口参数对出口空气温度和含湿量的影响曲线。结果表明：空气出口参数与空气人口含湿量、温度和流量、溶液人口温度和浓度几乎呈线性变化;当溶液入口流量达到2．5kg／s后,空气出口参数的变化趋于平缓。     

溴化锂吸收式制冷系统溶液热交换器的传热性能研究

以板式溶液热交换器为例，建立物理数学模型。通过对模型的求解，得到溶液热交换器在不同流速下的传热特性。计算结果表明，提高溶液热交换器中的溶液流速可以提高其传热系数，但会导致溶液的进出口温差减小，使溶液间换热不充分。设计溶液热交换器时可根据设计要求与文中计算结果选择不同的溶液流速。     

地埋管换热器变热流工况下换热模型及其试验验证

地埋管换热器实际运行时,热流总是变化的。为了研究变热流模型的正确性,本文讨论变热流下叠加原理在无限长线热源模型中的应用,以及此模型下地埋管换热器进出口水温的理论解。先保证热流恒定,对上海市某别墅地源热泵项目进行现场实测,将测试得到的相关参数作为已知。待岩土温度恢复到初始值时,进行变热流试验,通过变热流模型计算的进出口水温与实测的进出口水温比较,相对误差基本小于2％,最大误差不超过3％。     

Effects of liquid refrigerant injection on the performance of a refrigeration system with an accumulator heat exchanger

Liquid refrigerant injection technique can be a very effective method for controlling subcooling and the compressor discharge temperature of a refrigeration system at high ambient temperatures. In this study, the effects of liquid refrigerant injection on the performance of a refrigeration system with an accumulator heat exchanger were investigated by varying the liquid injection rate at the conditions of constant expansion valve opening in the evaporator and constant total flow rate. During the tests, the ambient temperature was maintained at 43 °C. With the increase of the liquid injection rate, the subcooling at the inner heat exchanger outlet increased and the superheat at the accumulator outlet decreased. However, unacceptable results such as the increase of the compressor discharge pressure and decrease of the system performance were also observed depending on the control method applied. To obtain high system performance and reliability, optimum control methods for liquid injection in the accumulator heat exchanger are suggested. The liquid injection technique for the refrigeration system with an accumulator heat exchanger was found to be an effective method for controlling adequate subcooling and the compressor discharge temperature of the refrigeration system at high ambient temperatures.